Jetting a KDX220

[skipro3]

1999KDX220
Currently jetted: Pilot-38, Main-145, JetNeedle-R1173L 2nd clip notch, 2 turns out on air screw.
Removed air cover, UNI filter, FMF KG-35 Woods pipe, TurboCoreII sparkarrester, Stock Reeds. 40:1 w/Maxima Super M. Typicaly run at approx. 4000 ft elevation. This is currently rich.
Adding Boyesen Power Reeds
Change to: Pilot-35, Main-140, JetNeedle R1173L 1st clip notch.
Does this sound too lean? I am told by the JustKDX site that when you add Boyesen reeds to lean out the Pilot and Main one size. I'm already rich so if I add reeds and lean out jets 1 size I would still be rich, therefore I'm dropping the main 2 sizes. The pilot isn't offered any smaller than 35, one size down from where I am now. Then there's the Needle. What would be the next leaner needle?
Any thoughts are appreciated.

 

[tedkxkdx]

The next available leaner needle is a R1172k. I live at lower than sea level, so I cannot give you all the insider information. But, you are not explaining why you think the bike is running rich and have you done jetting checks on each circuit of the carb or just changed the whole lot at one time? Maybe some circuits are not rich. Some changes depend on your typical riding style and where on the throttle your bike is running most of the time. Isolate what is rich and get back with us on it. I bet all the bomb craters make nice jumps.

 

[skipro3]

I would have thought the next available leaner needle was 1174M. Going from 73 to 74 is a larger diameter, so less fuel, and L to M is going longer on the needle, just like moving a clip up makes the needle longer and leans out. I believe it is running rich for two reasons, I ride tight woods and very rarely go past 3/4 throttle. When motoring along on a short staightaway at around half throttle, the bike's exhaust note sounds raspy and not clean, if I put it under a load, like more throttle or uphill, or short shift, it clears up. Plugs always look wet with lots of built up black crud on them. There is a booooog sound out of the exaust when building up rpms while under a heavy load like a steeper hill climb until the rpms have built up. I figured I would adust the pilot jet and main jet down one size since JustKDX says it is nessessary when adding Boysen Power Reeds just to stay even, then go one more size down on pilot and on the needle position to lean out enough to correct richness. With the needle position change, I no longer have any room to adjust and wanted to change needle size so that I would be back on the middle clip for fine tuning elevation and atmospheric daily changes.

 

[canyncarvr]

OEM (kawi) needles:

73L = 2.735 diameter, 39.15 L1
72K = 2.725 diameter, 38.60 L1

The second needle is more rich in a couple of ways, as you (skip) say.

The L1 of the first needle is an interpolative guess, cuz there is no direct cross.

From reading your post, however, I'm sure you know that.

With the bike in generally sound mechanical condition, jetting isn't about the numbers...it's about what's right for your bike, your environment and your riding style.

The 'one step leaner' doesn't really apply overall when you're talking about needles. It depends on where you want the 'step' in your throttle position.

From 1/8-1/4 throttle?...change the diameter
From 1/4-3/4 throttle?...change the L1

(This info from mxsouth keihin needle guide chart)

re: 'When motoring along on a short staightaway at around half throttle, the bike's exhaust note sounds raspy and not clean...'

Don't know what it sounds like, but you're describing a situation where the engine is going to be 4-stroking. With the addition of '.. it clears up' under load, I wonder if that is what you're referring to.

You will never get a 2-stroke to run under light load without 4-stroking. If you do, you'd better turn it off quick, cuz something is wrong! That's the sound of a happy 2-stroke!

The 'raspy' note part is what you do get with a sharply jetted bike. It sounds like the note is right at the end of the pipe as opposed to being buried under a bunch of metal.

blah blah blah...

The point is only you can correctly jet your bike for your situation. Set your main using a WOT plug chop test with a subsequent correct evaluation of your spark plug.

http://www.dirtrider.net/forums3/showthread.php?s=&threadid=60392&perpage=20&display=&pagenumber=1

Other circuits are set by the seat of your pants/throttle response. You will not get any sense of 'correct' jetting on the needle using a plug read.

Generally, the air screw going 'long' (out say 2.5 or more) is a sign of a too rich pilot jet. Going 'short' (say less than 1 out) is a sign of a too lean pilot.

Unfortunately, there are a number of situations where that doesn't apply. ;)

Didn't I say blah blah blah already?

Must be a lack of reasonable questions to respond to of late........

So....sounds like you know what you're doing and why. So just do it! Never a good idea to jet 'by the numbers' or 'because someone said'.

Check out the RB carb thread in the archives. JD has a ton of good jetting info there. Also consider his (JD's) jetting guide. You can graph five needles at a time for fuel flow characteristics. Check it out HERE

Rather than sticking with the B taper needle, consider a steeper slope (say a C, or 1'34" º) with a larger diameter. Something along the line of a CEL with the oem 5mm cutaway TV, maybe.

Good Luck!
God Bless you and your compatriots (based on your ID anyway).
Give saddam a kiss for me! ...if yanno what i mean.....

 

[skipro3]

Thanks canyncarvr!
First, let me just say, it is my thoughts and prayers that are in Iraq with my niece, 2 nephews, and 5 (ouch!) co-workers. God's speed to you all, and thank you for what you are doing.
Your information is just what I was looking for. I thought I would play with my jetting first, before looking into RB Design modification. Anyone out there with experiance with that on a 220? My final goal is to have tractor like torque and not worry too much about being in the right gear. (And not burning up the engine by running lean.) I was also wondering about running a range hotter on the plug. Is that an easy method of covering a slightly rich jetting, say on a ride that takes me from 4000 ft elevation to 6500 ft? I was thinking I could just swap a plug when I get a little higher. I've also messed with adding additional oil to the premix to lean out the gas but it ends up messy on the exaust. I remember my MX racing days back in the early 70's. Those things were like a light switch, on or off, and heaven help you if you missed a shift. I'm now just getting back into dirt now that my kids are through college and I have some change in my pocket. Thanks again for your input.

 

[canyncarvr]

It helps to send stuff before a tcp/ip stack reconfig/reboot........:(

Gotta hate it when your job gets in the way of DRN......???

A recap..........

re: heat range
I presume you mean a '7' vs: an '8'

Yep. 'Cover' is a good word.

You're fouling plugs? An NGK tech told me that they spec an '8' for the kdx for a reason.....because it's the correct plug! A change of one step in heat range will make a corresponding temp change in the engine of 50-80º or so. That might not be a desireable thing.

Consider a fine wire plug of the correct heat range...say a BR8EG. It will outperform the ES in marginal (poor jetting) situations.

re: 45-6500' el. change
That's not a huge change. No reason you should have to re-jet for that.

re: adding oil to lean
You got that right! A lot of riders refer to that as going 'richer', and if a point is made about it, an argument ensues. Oh well.

Another reason I gather from what you post that you'll get this sorted out to suit you soon.

Cheers!

Oh..re: not worrying about the 'right gear'.

Consider dropping a tooth on the front, from 13 to 12. If you don't spend much time in high gear doing 70mph, you'll appreciate the bottom end.

 

[skipro3]

Thanks for your reply!
I'll work response from last to first. I have gone from 13 tooth to 12 tooth on the countershaft. I forgot to mention it. If I'm currently running premix at 40:1, how much leaner would 32:1 or 16:1 make my jetting perform? I think I could use this as a fine tuning method to test and see which direction I am needing to go for small changes, or on a day when it gets hot and the air thins out a bit. (I learned that the hard way when attempting to lift a helicopter off at 8200' after landing with a nearly full tank in the early morning and trying to leave at mid afternoon. If anyone wants a good couple of deep cycle batteries, I know a spot in the forest where you can find them. Shedding load was a better alternitive to waiting for the temp. to drop). I am going to get those plugs right away. I've read here that B8ES might damage CDI units compared to BR8ES. Why is that?
I added the Boyesen #607 reeds, dropped the main from 145 to 140, dropped the pilot from 38 to 35, dropped the needle from the #2 slot to the #1 slot. Did a WOT throttle chop. A medium gray ring at the base of the insulator. I ran around my property for about 15 minutes and read the plug again. A slightly darker ring at the base and a light to medium gray on the rest of the plug, very uniform. No oil or spooge or wet at all. Air Screw out 1 full turn. Any more out and it doesn't matter, any more in and it slows down idle speed. A quick twist of the throttle has a lag from very low rpms., but fan the throttle three or four times and it has a note that sounds like it wants to kick some other bike's ass. Good! Any ideas about the "off the bottom" lag? When climbing a steep hill lugging at low rpm's, this thing pulls like no one's business! I am verry happy. There was tall grass on the hill, 3/4 way up I hit a rock about 12" tall. In second gear, chopped throttle when the front end lifted, 1/8 throttle as the rear tire touched the rock and front was starting to come back down, motored over without a glitch. Continued to the top without clutch, shifting, even sat down to enjoy the view!
By the way, when getting up to terminal velocity on the WOT chop test, I discovered that I must sit forward in the first 3 gears or this baby is going to loop on me, it is that powerful. Power pull was very even feeling throughout the rpm band as I shift through the gears and modulated throttle. Other than the lag from a dead idle to WOT for the first few hundred rpm's, I think I've got it! Thanks for the moral as well as technical support. I hope other 220 owners out there experiment with their torque monster and write in their findings. Later!

 

[canyncarvr]

re: fine tuning method (oil add)
Quite the pain. You'd never know what you were dealing with unless you completely drained the tank and started over with a 'changed' mixture. Much easier to change jetting. Yeah, you can fine tune that way..but that would be getting pretty picky about it. Run 40:1, jet to suit and be done. imo

You can compare the volumes of fluid and figure a percentage of change. ugh.


re: I've read here that B8ES might damage CDI units compared to BR8ES. Why is that?

Radiated noise from the hi-V field collapsing in the antenna (spark plug wire). Not anything I've ever heard of being a known issue with the kdx. I've run non-R plugs and not noted any difference. Still, I do use 'R's as a matter of caution.


re:dropped the needle from the #2 slot to the #1 slot
A long distance WAG (and therefore relatively worthless) ...but I'd go back to #2.


re: Did a WOT throttle chop. A medium gray ring at the base of the insulator

It's the thickness of that ring that shows the A/F mixture. That info is on the previously mentioned link......

re: Any more out and it doesn't matter, any more in and it slows down idle speed. A quick twist of the throttle has a lag from very low rpms

High idle is a starting point for the AS. Likely it will end up further in to be correct (best throttle response. Read, 'no lag') Seeing as your headed 'in' from 1T out, you're getting to a 'too lean' pilot indication.